The Pinnacle

Earth had been devastated by a genetic catastrophe. The survival of the human species at risk, the remnants of Earth's civilization constructed the starship Pinnacle. Only the best were chosen to attempt the mission; traveling to a distant star that had been identified as having an earth-like planet. After years in cryogenic stasis, the colonists aboard the starship arrived at their destination. They were young and optimistic. They named the planet "Eden". Eden was a world they would have dreamed if dreams could come true.
Casey Conklin is the only old man in the colony. Guardian/physician, he spent his life watching over the youths frozen in cryogenic stasis. Unfortunately, the years of solitude have driven Casey insane. Even though his insanity has been medically treated, the other colonists sense a difference in him.
Who has the more accurate grasp of reality? Is it the crazy old doctor, the hundreds of youthful colonists, or neither? What is reality?